1. Field
The present disclosure relates to a control method of a power train system.
2. Description of Related Art
As is generally known, a power train system of a vehicle includes a power generator for generating a driving power, a power converter for converting the torque and speed of the driving power generated by the power generator, and a power transfer unit for transferring the driving power, of which the output torque and speed are converted by the power converter, to a plurality of wheels.
The power generator may be installed in an internal combustion engine based on the combustion of fossil fuel, a motor engine based on the supply of electric force, a hybrid engine having an internal combustion engine and motor engine combined therein, and other types of motors.
The power converter generally includes a torque converter for converts the torque of a driving power outputted from the power generator and a transmission for changing a rotation speed.
The power transfer unit includes a differential gear and an axle shaft. The differential gear receives the driving power of which the output torque and speed are converted by the power converter, and the axle shaft transfers the driving power distributed by the differential gear to left and right wheels.
In general, a clutch system is further installed between the power generator and the power converter. Theoretically, the clutch system may be installed between the power generator and the power converter as described above, installed between the power converter and the power transfer unit, or installed between the power transfer unit and the left and right wheels which finally receive the driving power.
The clutch system may be disposed between parts which transfer and receive a driving power, in order to temporally block a transfer of the driving power. Therefore, the clutch system allows a vehicle to smoothly repeat stopping and running, without stopping the power generator.
In the case of a commercial vehicle, the clutch system may be installed to interrupt power between the power generator and the power converter, in order to minimize the consumption of energy generated by the power generator.
However, the position of the clutch system does not need to be limited. In many cases, the position of the clutch system may be changed depending on the types and features of vehicles to which the clutch system is applied. That is, a commercial vehicle and a heavy equipment vehicle used for a special operation are different from each other in terms of a required torque and required driving speed. Therefore, since each of the vehicles has significantly different driving efficiency and operation efficiency depending on the characteristics thereof, the structures of the power generator, the power converter and the power transfer unit need to be changed and designed according to the characteristics of each vehicle.
Depending on the characteristics of each vehicle, the design change of the power generator, the power converter and the power transfer unit is conducted in a different manner. Therefore, the power generator, the power converter and the power transfer unit are inevitably designed by a plurality of manufacturers, which makes it difficult to design an integration structure.
Furthermore, since the driving power outputted from the power converter must be distributed and transferred to the left and right wheels, the driving power is transferred through a bevel gear connected to the differential gear connecting left and right axle shafts.
More specifically, the bevel gear has a rotating shaft (hereafter, referred to as ‘bevel gear rotating shaft’) which is horizontally installed in the longitudinal direction of a vehicle body, and the left and right axle shafts are horizontally installed in the side-to-side direction.
At this time, since the bevel gear must be engaged so as not to significantly deviate from the central axis of a beveling gear installed on the differential gear, the design of the bevel gear rotating shaft for the axle shafts is considerably limited. In other words, since the bevel gear rotating shaft and the beveling gear are engaged to switch the direction of a driving power to a substantially orthogonal direction, a general spur gear engagement is unstable, and a spiral gear engagement is established. Therefore, the bevel gear rotating shaft and the rotating shaft of the beveling gear must be designed to be positioned at substantially the same height. When the bevel gear rotating shaft and the rotating shaft of the beveling gear are designed to have a predetermined height difference therebetween, the slopes of the tooth profiles of the bevel gear and the beveling gear must be increased. However, there is a limitation in increasing the slopes of the tooth profiles of the bevel gear and the beveling gear.
As long as the bevel gear is installed at the leading end of a propeller shaft including a universal joint coupling, the design of the vertical height difference between the bevel gear and the axle shaft has a tolerance to some extent. However, since the original function of the propeller shaft is to absorb a vertical height difference caused by a suspension system, it is not easy to secure a degree of freedom in design beyond the function.
Recently, the above-described power train system of a general vehicle is just applied to a heavy equipment vehicle such as a forklift truck. Korean Patent Registration No. 10-0425277, which had been filed by the present applicant and registered in the Korean Intellectual Property Office, is a representative example.
The system according to the patent document has been devised to not only minimize noise and vibration of an engine, which may occur when a power train system of a general vehicle is applied to a heavy equipment vehicle such as a forklift truck, but also minimize the turning radius of a heavy equipment vehicle. According to the patent document, a transmission and clutch system may be integrated in an axle hub of an axle shaft in order to improve braking performance, and the design of engine mounting and axle mounting may be facilitated through a compact structure.
However, when the transmission and the clutch system are integrated in the left and right axle shafts having different gears installed therein, the load may be concentrated. In this case, the structure must have a strong housing to protect the respective components, and the engagement between gears must be performed with precision. Thus, the manufacturing cost is significantly increased.
Furthermore, since the bevel gear is directly engaged with the beveling gear installed on the differential gear, the whole length of the power train system including the propeller shaft is increased to limit the degree of freedom in structure design.